The invention resides in the field of molded bodies manufactured from a mass comprising at least natural polymers, and in particular starch, and water.
The molded bodies have a blown, foamy structure. More particularly, the foamy material always comprises at least three parts: two relatively dense layers on the outside, which as it were form a skin, and between them a foam structure as core layer. The dense layers are firm and strong and consist of substantially closed, small cells. The foam structure of the core is generally open; the cells have burst to allow the gases evolving during the manufacture, for instance water vapor or carbon dioxide, to escape. Generally, the cells have a firm and solid cell wall due to the relatively high pressure and temperature in the mold or die during the manufacturing process.
These products can be manufactured in many manners, for instance according to the methods described in WO-A-95/20628, NL-A-1004138 and WO-A-96/30186.
These known methods start from a mass or batter which substantially consists of a mixture of modified or non-modified biopolymers, and particularly starch, and water, to which processing aids and additives for influencing the properties of the finished product are added. This has advantages particularly if fibrous material is added thereto to increase the dimensional stability and reinforce the finished product.
Generally, such batters comprise, for instance, 500-1500 parts by weight of starch or starch derivatives, 0.5-50 parts by weight of xanthan gum, 5-250 parts by weight of a reactive siloxane and 0-300 parts by weight of an inert filler in water. Additionally, preferably 0.5-50 parts by weight of a salt are further included, and 0-25 wt. % of fibers calculated on the weight of the complete batter mass.
The above embodiments are applicable for the present invention, yet should not be construed as being limitative in this context. Other batter compositions on the basis of water and natural polymers, in particular starch or starch derivatives, can likewise be used. In this respect, it is within the scope of a skilled artisan to set optimum processing conditions, such as pressure, temperature and residence time, depending on the batter and the molding apparatus to be used and within the framework of the invention.
In the known methods used for forming foamed molded bodies to which the present invention is directed, a starch or starch derivative is in each case used, in practice.
Starch is usually obtained from crops having a high starch content, in particular from cereals, including rice and maize, and from potatoes. The parts of these vegetable sources that possess high starch contents are washed and subsequently ground. From the ground plant parts, the protein fraction can then be separated, when necessary. After that, the starch granules are separated from fibrous material present and from other impurities by means of, for instance, sieves and/or hydrocyclones. This so-called starch refining requires much water. The obtained and washed starch granules are subsequently dehydrated with a vacuum filter and dried with hot air of, for instance, about 120xc2x0 C.
When the molded bodies are not intended for consumption, relatively crude starch may usually suffice.
European patent application 0 474 095 concerns a method wherein starch-containing natural products are used in starting substances of molded bodies. For starch-containing fruits and potatoes, a pre-drying step is preferably used. Next, a pre-heating step is performed which, depending on the water content, takes place at a temperature below the glass transition temperature or at a temperature above 80-90xc2x0 C. This results in the formation of a plastic or gelatinized product which can subsequently be shaped.
Nowhere, a link is made between a faster and more homogeneous gelatinization and the use of undried, crude vegetable material. Further, no reference is made to the removal of protein-containing material and/or salt so as to limit the disadvantageous influence during the baking process in the mold.
DE-OS-42 11 888 describes molded bodies manufactured from dough or batter prepared from complete plants. The use of only plant parts that have a starch content of at least 50 wt. % calculated on the dry substance and the advantages involved is neither described, nor suggested, and neither is the separation of protein and salt.
It is an object of the present invention to further optimize the method for manufacturing molded bodies on the basis of natural polymers, in particular starch and/or starch derivatives. In particular, there is a need for a method in which the required gelatinization can be performed more quickly and preferably more homogeneously. Moreover, there is a need for a method in which, if additives are used for improving the properties of the finished end product, such as cross-linking agents, these additives are distributed more properly, in particular more homogeneously, between the different starch chains. A further object is to cause the baking process to proceed in a more controlled manner.
Surprisingly, these objectives can be accomplished by applying in the batter starch that has not been subjected to a drying step.
More in particular, the invention relates to a method for manufacturing a molded body having a blown, foamy structure, wherein a mass comprising a suspension of at least starch, starch derivatives or mixtures thereof in water, is pressurized in or through a mold and the mass is heated in the mold in a manner such as to give rise to at least cross-linking of the starch, the starch derivatives or the mixture thereof, wherein the mass in the mold is brought at least to the baking temperature, characterized in that the suspension is prepared from vegetable material which has not been subjected to an artificial drying step and which contains at least 50 wt. % of starch, calculated on the dry substance, which vegetable material is ground to particles of a suspendable size.
In addition, the invention relates to the use of ground vegetable material, which vegetable material has not been subjected to an artificial drying step and which contains at least 50 wt. % of starch, calculated on the dry substance, which vegetable material is ground into particles of a suspendable size, in a mass subjected to a thermal molding step under pressure, to effect a quicker and more homogeneous gelatinization.
Further, the invention relates to the application in which, further, at least one additive for improving the properties of the product to be formed is added to the mass, to obtain a homogeneous distribution of the additive in and between the starch chains of the vegetable material that has not been subjected to an artificial drying step. Via this application, in particular, better reaction possibilities for the additives are created.
In this description, xe2x80x9cgelatinizationxe2x80x9d is understood to mean a change of starch and/or starch derivative from a slightly or completely loose granular or comparable granulate form into a form in which stretched starch and/or starch derivative chains are present, which chains are interconnected only slightly, if at all. That is to say, there occurs a transition of starch or starch derivative from a solid form, a colloidal solution or suspension to a more homogeneous fluid mass. In this description, the term xe2x80x9cgelatinizingxe2x80x9d is synonymous to terms like xe2x80x9cgellingxe2x80x9d, xe2x80x9cgellatingxe2x80x9d and the like.
In this description, by xe2x80x9cbakingxe2x80x9d is understood to mean a method in which both gelatinization and cross-linking occur, at relatively high temperature and/or pressure. As a result, the formation of gas arises relatively soon, so that bubbles are already formed prior to or during gelatinization. Due to inter alia the high pressure adjacent strongly heated parts, the polymers cross-link quickly when using a mold or like baking form with a temperature at or above the baking temperature.
These baked products have a core with relatively large cells, enclosed between skin parts with relatively small cells. The cell walls have a relatively high density. Such a baked product therefore has a sandwich-like structure.
In accordance with the invention, in the batter which, according to otherwise known methods, can be formed into a foamed end product, ground vegetable product is applied as at least a part of the required starch source. The vegetable products to be ground are products directly obtained from nature and have a relatively high starch content. More in particular, these products should have a starch content of at least 50 wt. %, preferably at least 60 wt. %, and more preferably at least 70 wt. %, calculated on the dry substance.
Examples of such vegetable products are starch-containing tubers and roots, seeds, fruits and grasses. More specifically, potatoes, tapioca, sweet potatoes, arrowroot, sorghum, waxy sorghum, cereals, rice, maize, sago, canna, pulses like peas, beans and lentils, unripe fruits such as apples and green tomatoes, and bananas.
In the following diagram, a number of supplementary data in respect of a number of highly preferred starch sources are given (in percents):
It is important that the above vegetable products be subjected to an artificial drying step only to a highly limited extent, if at all, which means that these vegetable products are substantially ground in the condition in which they are obtained in nature or, optionally, in the condition in which they are dried on the air, possibly in coarse pieces, yet in unground form.
Without wishing to be bound to any specific theoretical explanation, it is assumed that the use of suspendably ground vegetable products as starch source yields the advantages according to the invention, because in this form, the starch granules are practically undamaged and the separate starch chains are in undisturbed equilibrium with water. More in detail, it is assumed that when starch is obtained from said vegetable sources in a more refined form, starch granules shrink and the pore volume in the granules decreases during the required drying steps. In particular, a dried skin is formed on the outside of the dried starch granules. This involves hydrogen bridges between water molecules and starch chains as they are found in the natural cell environment being at least partially broken and converted into starch-starch interactions.
When dried crude starch, which, when exposed to the atmosphere, usually still contains 15-25 wt. % of moisture, is introduced into an aqueous medium, water molecules can penetrate into the granules slowly and to a limited extent, mainly because the pore volume in the dry granules is relatively low, while below the gelatinization temperature, which is about 55xc2x0 C., the starch-starch interactions formed through drying substantially do not break.
When after obtaining, the starch is refined first, the water-absorbing capacity is limited even further. Indeed, the refining involves an exchange between naturally present monovalent sodium and potassium ions and bivalent ions present in hard water, in particular calcium and magnesium ions. This exchange, which is in fact a displacement, causes a physical cross-linkage between the separate starch granules, which cross-linkage impedes the swelling of the granules.
Both above-mentioned cross-linking effects, viz. the starch-starch interactions in the granules and the cross-linking of individual granules relative to each other due to the presence of bivalent ions, give the starch granules a configuration or structure that swells with difficulty, while the gelatinization of the granules is moreover slowed down. However, as in the method according to the invention, only a short (reaction) time is available in the mold, particularly in processes on an industrial scale, it is highly important to limit these physical cross-linking effects as much as possible.
In the method according to the invention, the above physical cross-linking effects substantially do not play a part, because the starch granules are located in an optimum aqueous medium, viz. the natural water environment.
This water environment enables a fast gelatinization. After gelatinization, the individual starch chains are properly accessible, which enables the derivatization reactions on the starch chains to be performed highly homogeneously in the mold. In this manner, a highly homogeneously derivatized product can be obtained, which is not possible with a starch subjected to a drying step and/or a refined starch, because of the reduction of the pore volume and the formation of a dried skin during the drying steps necessary for obtaining starch. There, reagents can substantially only contact the outside of the granules.
More in particular, during derivatization in the mold with a starch subjected to a drying step and/or a refined starch, which therefore possesses a large number of physical cross-links, the gelatinization may occur too slowly, so that a derivatization reaction may take place before the gelatinization is complete. As a consequence, the reagents substantially only contact the outside of the partially gelatinized granule. Moreover, the derivatization reaction which is already in process may impede the further gelatinization.
Also when a priorly prepared derivative is added to the batter suspension, no homogeneous product is obtained. In that case, the reaction during the derivatization prior to use in the mass occurs particularly in the outer skin of the starch granules. Thus, for instance for the specific derivatization for forming cross-links, a priorly made cross-linked derivative has bindings only-between starch chains at granular level, while specific groups will moreover be coupled only to the outside. After eventual gelatinization of such derivatives in the mold, no homogeneously cross-linked and/or derivatized product results.
As mentioned hereinabove, in the method according to the invention, it is possible to cause a derivatization reaction to take place homogeneously in the mold.
Derivatization reactions that can suitably be performed in the method according to the invention are, for instance, the provision of reactive cross-linkable groups, esterification reactions, such as acetylation reactions utilizing acetic acid anhydride and adipic acid, and etherification reactions, such as benzylation reactions utilizing C6H5CH2Cl, which reactions yield a more hydrophobic product. The required quantities depend on the starch type to be derivatized, the type of derivative, the intended object and the apparatus whereby the molded bodies according to the invention are-manufactured. This can be experimentally determined by a skilled person in a simple manner.
An essential step in the method according to the invention is the grinding of the starch-containing vegetable raw materials. These grindings can be performed in any industrially applicable grinding machine for this type of raw materials, to a grinding degree which yields a product that can substantially be suspended. This can be experimentally determined by a skilled person in a simple manner.
Typically, grinding involves the formation of a suspension which sags when it is let stand for a while, for instance 1 hour. The supernatant mainly consists of water containing a number of water-soluble compounds, and in particular water-soluble protein and salts. It is advantageous to substantially remove this water with the compounds dissolved therein utilizing a known technique, such as decanting, centrifuging and filtering. Thus, in particular protein and salt, which may usually have an adverse effect on the baking process in the mold, can be removed.
Accordingly, a preferred embodiment of the method or use of the invention is characterized in that after grinding, the suspension formed is allowed to sag, after which the supernatant thus formed is removed at least partially, for instance for more than 50 vol. %, preferably for more than 80 vol. %, and possibly completely.
Generally and advantageously, a quantity of fibrous material will already be present the ground substance fraction.
A further object of the invention is to provide an apparatus for the manufacture of foamed products, in which the supply of the starting materials is simple, in which the manufactured products are simple to remove from the mold, which allows a relatively great freedom of design and in which the manufactured products have a good dimensional stability and exhibit relatively good resistance to different conditions, including moist environments and temperature fluctuations, which products can moreover be integrated into a (paper) reuse flow ((paper) recycling). To that end, an apparatus according to the invention is characterized by the presence of at least one forming mold and at least one apparatus for cutting up and/or grinding the vegetable material, means being provided for making a mass from at least the cut up or ground natural plants and feeding the mass into or through the at least one mold; or by the presence of at least one mold having at least one mold cavity and supply means for supplying a biopolymer, in particular starch-containing mass, into the or each mold cavity, while adjacent the supply means, feed means are provided for introducing additives into the mass directly before or during the supply of the mass into the at least one mold, in particular agents suitable for entering, in the mold, into chemical and/or physical reactions with components of the mass; or by the presence of at least one mold having at least one extrusion orifice and supply means for supplying a biopolymer, in particular starch-containing mass, into the at least one extrusion orifice, while adjacent the supply means, feed means are provided for introducing additives into the mass directly before or during the supply of the mass into the at least one extrusion orifice, in particular agents suitable for entering, in the mold, into chemical and/or physical reactions with components of the mass.
In this application, mold, should at least be understood to include platen sets, baking molds, injection-molds, extrusion molds and compression molds.
Owing to the supply of the mass from which the or each product is to be formed, preferably at a temperature which is below the gelatinization temperature, the supply of the mass can be realized in a simple manner, for instance via pumps and pipes. Moreover, a stock of the mass can be priorly prepared and be fed to a processing apparatus directly from a storage tank. By subsequently passing the mass under pressure into or through the mold and only heating it in the mold, it is ensured that the mold is always filled sufficiently. The flow path, i.e. the or each path traversed by the mass to and in the mold, can then be long to very long with respect to the cross sections of the passages. Only in the mold, the eventual gelatinization of the natural polymers occurs and then cross-linking of those polymers.
The feed of additives, for instance reagents for derivatization reactions, in or adjacent the supply means, offers the advantage that any chemical and/or physical reactions between the mass and the additives take place only at a late stage, for instance only in the mold. As a result, derivatization can for instance occur in the mold, with the mold acting as reactor vessel. Moreover, this permits the flow properties of the mass to be maintained.
Due to the cross-linking that occurs, a firm product is obtained. The natural polymer, in particular the starch, provides for a relatively firm skeleton extending around preferably continuous cells that form in the mold due to moisture or another blowing agent which, as a result of the heat in the mold, attempts to escape from the mass and forms bubbles caused by the pressure in the mold. As a result, the product obtained has a blown foamy structure. Since the natural polymer provides for a relatively stiff jacket, the thus obtained product is dimensionally stable upon exiting from the mold. Depending inter alia on the extent of cross-linkage, the product obtained is more or less flexible.
Since the mold is heated and not the mass prior to it being introduced into the mold, the temperatures in the mold can be properly controlled, both for the mold as a whole and for each separate portion thereof. As a result, products can be manufactured with different and varying wall thicknesses and with different mechanical properties. In fact, by heating more or less and/or for a longer or shorter period and adjusting, for instance, the pressure, for instance the extent of cross-linkage of the polymers can be controlled locally, so that the mechanical and physical properties are influenced. This can be determined by a skilled person in a simple manner.
Heating the mass up to baking temperature, hence in excess of 100xc2x0 C., offers the advantage that the occurrence of fungoid growth is prevented or at least substantially decelerated.
The products obtained with a method according to the invention are relatively strong and compression-resistant, shock-proof and relatively elastic, insulating and can be reduced without involving fragmentation. After use, the products can be incorporated into an existing waste flow for, for instance, composting or, more advantageously, into a paper-recycling flow.
In this respect, the presence and/or addition of fibers, in particular natural fibers, offers the advantage that the products are more dimensionally stable after being manufactured and remain form-retaining, and also under moist conditions can have an increased tear-resistance, strength and flexibility.
By using natural fibers in products according to the invention, in particular fibers of, for instance, annual crops and/or recycled fibers such as cellulose fibers from paper and wood waste, significant advantages in terms of environment and manufacture are achieved. For instance, the emission of harmful substances is reduced, if not prevented, both during the manufacture and during the waste processing. Since no fossil resources are used in the products, the waste processing thereof will not cause any permanent CO2 increase in the atmosphere, so that these products do not contribute to the so-called hothouse effect.
A further significant advantage achieved through the addition of the fibers is that the resulting product retains its original shape and properties longer than it does without fibers. Although composting, i.e. the biological degradation process, proceeds relatively slowly, which renders the product less suitable for incorporation into a flow of vegetable, fruit and garden refuse, the product is thus sufficiently durable for serving, for instance, as packaging material, also if the articles packaged therein are for instance stored for a long period and/or are sent, or under unfavorable conditions, such as high temperature and/or high air humidity. Upon further preservation, products manufactured according to the invention are suitable as construction elements, building parts and the like. These products are durable, light, moldable, insulating and have a sandwich construction.
In filling batter compositions known from the prior art, inert fillers may be incorporated. According to the present invention, it has been found that it is advantageous to select the content of inert fillers to be lower than 50 wt. %, in particular lower than 20 wt. % and preferably lower than 15 wt %, calculated on the total weight of the batter. At higher contents of inert fillers, contamination of the mold occurs and the resistance to moisture may be reduced.
A product manufactured in accordance with the invention is generally self-extinguishing, while comparable products manufactured from, for instance, (paper) pulp are relatively combustible. Moreover, the manufacture of such pulp products is labor-intensive and costly, the products are less strong, heavy, little resistant to, for instance, high temperatures and moisture, and exhibit little freedom of design. A number of these and comparable drawbacks occur with comparable products manufactured from plastic such as polystyrene, foam and the like.
Further, a product obtained from the method or use according to the invention-has the advantage that it causes no problems in respect of static load, so that in particular electronic components and other charge-sensitive products can very suitably be packaged in products according to the invention.
The invention further relates to the use of an injection molding apparatus or extrusion apparatus for manufacturing foamed products and to products manufactured according to the invention.
Further advantageous embodiments of the invention are given in the subclaims.